Thromboembolic disease is a common human physiological disorder, with about 2.5 million cases per year arising in the United States alone. Thrombi are manifested by the partial or total occlusion of blood vessels by the formation of deposits of platelets, fibrin and other blood elements. Emboli are portions of thrombi that have broken away from the site of their formation and lodged in small blood vessels, such as the vessels of the lungs or the brain. Acute vascular diseases, including pulmonary embolism, deep venous thrombosis (DVT), peripheral arterial occlusion, myocardial infarction and other blood system thrombi constitute major health risks. Safe and accurate detection of the presence and location of intravenous thrombi in the human body is required for disease diagnosis, prognosis and effective treatment. Some forms of thrombosis, such as DVT, are virtually undetectable at early stages due to highly unreliable clinical signs. Because of the potential risk or morbidity and mortality, early detection and treatment of thromboembolic diseases are of paramount importance. Anticoagulant therapy is available for treatment of thromboembolic disorders, but poses additional risks such as hemorrhaging and thrombocytopenia. Therefore anticoagulants should not be used without a justifiable level of medical certainty confirming the presence of thrombi.